1997—2010年北京市大气降水离子特征变化趋势研究

依据北京市环境保护监测中心1997—2010年降水监测资料,分析北京地区降水中离子特征及变化趋势,阐明北京市降水污染现状及变化特征。结合北京市特有的气象条件、地形地貌和工业分布情况,分析污染物来源及污染变化趋势。研究表明:年度降水电导率呈现波动变化,降水污染严重程度依次为南部郊区>市区>北部背景点。北京地区大气降水中的主要阳离子成分是Ca²⁺和NH₄⁺,主要阴离子成分是SO₄^2-和NO₃^-。近年来SO₄^2-]/NO₃^-]比值逐步下降,污染类型由典型硫酸型发展为硫酸+硝酸混合型。阳离子Ca²⁺]/NH₄⁺]比值下降,碱性离子缓冲能力降低。9种离子各季节浓度变化趋势基本一致,由高到低依次是春季>秋季>冬季>夏季,这种季节变化特征与气象因素密切相关。相关性及聚类分析表明:NO₃^-与SO₄^2-存在很强相关性,说明其前体物SO₂和NO_X在大气中经常一同排放且进入降水途径相同;H⁺浓度不是由某个离子决定,是所有致酸离子和中和离子相互作用的结果,而NH₄⁺来源不同于其它离子,北京地区的氨存在其单独排放源。

Change of Anion Characteristics Analysis on Acid Rain in Beijing 1997~2010

Based on the data of acid rain during the period of 1997 to 2010 from Beijing municipal environmental monitoring center,taking lcoal weather,geographic and geomorphic conditions,and location of industries into account,this paper will illustrate the current situation and characteristics of acid rain pollution in Beijing area. The main findings include:The conductivity of precipitation fluctuated annually; trends of air pollution for different point locations are similar since 1997,which is southern suburbs> downtown> northern suburbs. Conductivity is strongly correlated with ion concentrations and shows a power function related with the amount of precipitation.Ca²⁺ and NH₄⁺ constitute the main cations in precipitation,while SO₄^2- and NO₃^- constitute the main anions. The ratio ofSO₄^2-]/NO₃^-]has decreased gradually during the past years,the pollution source has changed from typical sulfuric acid pattern to combination of sulfuric acid and nitric acid. The ratio ofCa²⁺]/NH₄⁺] has kept decreasing,neutralization from alkaline ions became weaken. The variation trend of of monitoring concentration of nine types ions were similar,i.e.,spring> autumn> winter> summer. Thus,the temporal variation is closely related with seasonal conditions.The results of correlation and cluster analysis show a strong correlation between NO₃^- and SO₄^2-. It indicates that SO₂ and NO₂ are always emitted to the air together,and they have the same approach and mechanism to effect precipitation; Our research shows that the concentration of H⁺ is not determined by a fixed certain ion,it is effected by the interaction between all of the acidic ion and neutralization ion. While NH₄⁺ is supposed to come from other exclusive sources.